1. Field of the Invention
The invention relates to a parking brake system for vehicles, in particular passenger vehicles, in accordance with the preamble of claim 1.
2. Description of Related Art
A parking brake system of this type has already been disclosed in EP 0 710 595 A1. This known parking brake system has an adjusting unit which can be actuated, by means of a motor drive, for applying or releasing at least one actuating pull of a brake device of the vehicle. The drive is drive-connected to a component which is mounted such that it can rotate about a longitudinal axis and such that it is non-displaceable with respect to the longitudinal axis, while the component itself is coupled in a rotationally fixed manner to a telescopic device which is arranged such that it can be displaced in the direction of the longitudinal axis. The axial length of the telescopic device can be increased or reduced as a function of the direction of rotation of the component. A respective actuating pull is coupled to each axial end of the telescopic device, the actuating pulls being connected in each case to a brake of the brake device. The telescopic device of the known parking brake system is distinguished in that the drive causes two threaded rods which have an opposed thread pitch to rotate, the threaded rods being in engagement with the internal threads of corresponding sleeves which are mounted in a rotationally fixed manner. A rotation of the two threaded rods therefore results in the corresponding sleeves or the actuating pulls being displaced axially. This known parking brake system is formed in a fairly complicated manner with regard to the structural design and has a multiplicity of parts.
DE 42 05 590 A1 has already disclosed a further parking brake system for motor vehicles, having a foot-operated brake pedal. In this case, an additional adjusting unit having a motor drive is provided, the unit acting directly on the brake pedal via a coupling device. Pressing of a button, which is situated, for example, in the control handle of the vehicle transmission, causes the direction of rotation of the electric motor of the adjusting device to be reversed in each case, so that the brake pedal is pivoted downward or released upward again by the electric motor. The brake pedal is locked mechanically via the transmission, which is of self-locking design, of the adjusting unit. The parking brake system has an electronic control device with which the operating current of the electric motor can be detected and therefore information on the angle of rotation of the transmission spur gear and therefore on the braking force and the instantaneous travel of the brake cable displacement can be obtained. However, in the case of this known parking brake system failure of the motor drive may be a problem. If a plurality of brakes of the vehicle are to be actuated by means of the parking brake system, a further problem is that an uneven application of the actuating pulls may occur because of, for example, the brakes wearing at different rates.
The unpublished patent application 197 28 135.4 of the applicant furthermore discloses a parking brake system which is provided with two motor drives so that in the event of one drive malfunctioning, the parking brake system continues to be fully functional. However, this measure constitutes a considerable, technical outlay.
In contrast, the invention is based on the object of developing a parking brake system having the features mentioned at the beginning in such a manner that a technically uncomplicated, simplified design is provided. In accordance with a coordinated aspect of the invention, the intention is for the parking brake system to be mechanically releasable in the event of a fault or in the event of a failure of the motor drive.
The main object of the invention, in the case of the parking brake system having the features mentioned at the beginning, is achieved below by the features of claim 1. The telescopic device is formed by the hollow shaft, which is preferably designed as a splined shaft, and by a single spindle, threaded rod or the like, which is mounted rotatably in the hollow shaft. As a result of the hollow shaft being designed as a splined shaft and the gearwheel having a corresponding splined hub, the hollow shaft can be freely displaced, with regard to the gearwheel, in the direction of the longitudinal axis, there nevertheless being a rotationally fixed coupling between the gearwheel and the shaft. By this means, the structural design is simplified and the number of parts required reduced. As a result of the telescopic device or the hollow shaft and spindle being mounted in an axially displaceable manner on the component or in a floating manner in a housing of the parking brake system, there is a compensating action between the two actuating pulls for the two brakes, so that an even braking action of the two brakes is ensured. Moreover, the entire parking brake system is not subjected to a one-sided force action and, as a result, further high, mechanical loads on the parking brake system are avoided. The housing of the parking brake system is possibly acted upon merely by a differential force between the coupling points of the brake pulls, since the entire telescopic device is mounted in a floating manner in the housing of the parking brake system.